Axelrod: The Pliocene Verdi Flora of Western Nevada 97 



KATE PEAK ANDESITE 



From its type area in the Silver City region 20 miles southeast (Gianella, 1936), 

 Kate Peak andesite can be traced almost continuously into the Verdi basin, where 

 it is exposed chiefly in the Carson Range south of the Truckee River. The section 

 is largely one of interbedded agglomerates, mudflow breccias, and lavas. The ag- 

 glomerate-breccia phase of the Kate Peak is readily recognizable from a distance, 

 for it forms craggy outcrops. The section is typically gray to gray-brown in 

 weathered exposures, but fresh surfaces are light gray. The rocks are chiefly horn- 

 blende andesite in the area examined, with the breccia beds ranging from 10 or 20 

 feet, up to 50 or 60 feet thick. Cobble and boulder conglomerates which are from 

 3 or 4 feet up to 20 or 30 feet thick, and characterized by reworked andesite, are 

 scattered through the section. The pyroclastic phase increases in thickness to the 

 southwest, and in the Truckee River canyon south of Fleish, near the California 

 border, most of the section is composed of mudflow breccias and agglomerates. The 

 lavas are light to medium dark gray, and characteristically porphyritic. They 

 occur in units ranging up to several hundred feet thick, and are typified by several 

 prominent joint systems that make it difficult to take reliable attitudes. 



Along faults, hydrothermal alteration has locally affected parts of the forma- 

 tion. At several points near the marginal fault south of the river, as in sections 21 

 and 26, the section is quite bleached and shows up from the highway 2 to 3 miles 

 distant as light yellow to orange and reddish outcrops. Since the overlying Coal 

 Valley formation contains coarse to fine clasts derived from the bleached Kate Peak 

 rocks, it is apparent that alteration occurred before the deposition of the Coal 

 Valley formation, and that an unconformity separates them. 



Kate Peak andesite rests on all the older rocks in this area. Near Fleish, it lies 

 on granodiorite or on metamorphic rocks. To southward in the Carson Range, 

 outside the mapped area, it rests on Alta andesite. Total thickness of the exposed 

 section within the mapped area is in excess of 1,500 feet south of the river, and it 

 rapidly increases to the south and west to over 2,500 feet. The formation has 

 generally only moderate dips, ranging chiefly from 25° to 40°, though near major 

 faults it increases to 50° or 60°, and locally to vertical. 



On the basis of its interfingering relationships with the fossiliferous Mehrten 

 formation of the Sierra Nevada, the Kate Peak andesites were erupted chiefly 

 during a span of time ranging from the Mio-Pliocene transition (Early Claren- 

 donian) to the later part of Early Pliocene time (Late Clarendonian), with a 

 few spasmodic episodes extending into the early Middle Pliocene (Hemphillian). 



COAL VALLEY FORMATION 



Areal Relations 



The sediments in the Verdi area were mapped first by King as part of the Truckee 

 formation, and they have been considered to represent the Truckee by all subse- 

 quent investigators, including Louderback (1906), Anderson (1909), Buwalda 

 (1914), Hill (1915), Merriam (1916), Stirton (1939), MacDonald (1950; 1956), 

 and Thompson (1956) . Nonetheless, my comparative studies of the Verdi sediments 

 and the type Truckee formation, which lies 60 miles northeast, show that the 



